Having a tubal ligation does not increase your bodyweight. The recovery time for the surgery is around three to five days, and should not pose any form of long-term problem in your current diet or weight loss plan.
Once your doctor clears you back to normal activity, you'd lose weight the same way anyone else would. A healthy diet and excercise.
Having your tubes tied is not entirely effective, if you've gotten pregnant once with them tied chances are you can again.
They can get their tubes tied.
You should not be able to get pregnant. Just having your tubes tied would be enough to prevent pregnancy, especially if they were cut then tied (tubal ligation).
There is no need to remove the IUD before (or after) having your tubes tied. Leaving it in will ensure continuous protection.
Yes, having your tubes tied does not prevent 100% of pregnancies. My sister became pregnant 15 years after having her tubes tied.
There are no side effects of having your tubes tied and leaving an IUD in place. There is no pressing need to remove the IUD if you have other pregnancy protection.
Here the age is not important, but you have two or three children then you can go ahead and have your tubes tied for safety.